Ca2+-dependent inactivation of CaV1.2 channels prevents Gd3+ block: Does Ca2+ block the pore of inactivated channels?

Authors

Olga Babich, Rutgers New Jersey Medical School
Victor Matveev, New Jersey Institute of Technology
Andrew L. Harris, Rutgers New Jersey Medical School
Roman Shirokov, Rutgers New Jersey Medical School

Document Type

Article

Publication Date

6-1-2007

Abstract

Lanthanide gadolinium (Gd³⁺) blocks CaV1.2 channels at the selectivity filter. Here we investigated whether Gd³⁺ block interferes with Ca²⁺-dependent inactivation, which requires Ca ²⁺ entry through the same site. Using brief pulses to 200 mV that relieve Gd³⁺ block but not inactivation, we monitored how the proportions of open and open-blocked channels change during inactivation. We found that blocked channels inactivate much less. This is expected for Gd ³⁺ block of the Ca²⁺ influx that enhances inactivation. However, we also found that the extent of Gd³⁺ block did not change when inactivation was reduced by abolition of Ca²⁺/calmodulin interaction, showing that Gd³⁺ does not block the inactivated channel. Thus, Gd³⁺ block and inactivation are mutually exclusive, suggesting action at a common site. These observations suggest that inactivation causes a change at the selectivity filter that either hides the Gd³⁺ site or reduces its affinity, or that Ca²⁺ occupies the binding site at the selectivity filter in inactivated channels. The latter possibility is supported by previous findings that the EEQE mutation of the selectivity EEEE locus is void of Ca²⁺-dependent inactivation (Zong Z.Q., J.Y. Zhou, and T. Tanabe. 1994. Biochem. Biophys. Res. Commun. 201:1117-11123), and that Ca²⁺-inactivated channels conduct Na⁺ when Ca²⁺ is removed from the extracellular medium (Babich O., D. Isaev, and R. Shirokov. 2005. J. Physiol. 565:709-717). Based on these results, we propose that inactivation increases affinity of the selectivity filter for Ca²⁺ so that Ca²⁺ ion blocks the pore. A minimal model, in which the inactivation "gate" is an increase in affinity of the selectivity filter for permeating ions, successfully simulates the characteristic U-shaped voltage dependence of inactivation in Ca²⁺. © The Rockefeller University Press.

Identifier

34249803597 (Scopus)

Publication Title

Journal of General Physiology

External Full Text Location

https://doi.org/10.1085/jgp.200709734

e-ISSN

00221295

ISSN

00221295

PubMed ID

17535960

First Page

477

Last Page

483

Issue

6

Volume

129

Grant

0417416

Fund Ref

National Science Foundation

Recommended Citation

Babich, Olga; Matveev, Victor; Harris, Andrew L.; and Shirokov, Roman, "Ca2+-dependent inactivation of CaV1.2 channels prevents Gd3+ block: Does Ca2+ block the pore of inactivated channels?" (2007). Faculty Publications. 13434.
https://digitalcommons.njit.edu/fac_pubs/13434